Pelletizing and sizing drum



'like material.

v i. between the closely jammed surfaces. In order to join'iines together successfully by ballingor pelletizing, the many operating variables must'be ad- PELLETIZING AND SIZING DRUM Harold T. Stirling, Pittsburgh, Pa., assigner, by mesne assignments, to Stirling ration of- Pennsylvania Filed Apr. -19, 1963,- Ser. 1`\Io..274,251'y Sinterin'g Corpoiation, a corpo- 8 Claims. (Cl. 1 8--1 The present invention relates to an apparatus for the production -of sized, pressure-hardened balls or pellets from pulverulent material.

-Many' industrial processes result inftheproductionof a 3,210,772 Patented Oct. 5,1965

was a simple drum in the formv of a cylinder. This type of drum Ahad many disadvantages, for example, the pellet once formed had to work its.way through the length of the entire drum before it was 'discharged and'unpelletized tine material wasalso carried throughthedrum'. A special conveyor was necessaryfor vrecirculating these undersized finest-back to the feed end off the drum.V The pellets formed in this type of drum were not uniform in substantial amount of material in the form of line dust- Itis impossible to utilize vsuch .material without first processing the material into ksized agglomerates. Such pulverulent'material is becoming available in vast quantities.

Theequipment used to increase the.v particle size ofufine '1 ,-,ahas aratherv low retention'time thus causing low produc- I ytionand yielding insuicientlyllargepellets. In addition,

size `or shape and were too soft to possess sufficient mechanical strength for further processing. Another disadvantage of these drums is that they are extremely large and therefore consume a greatquantity of space.

Another typeof vpelletizing apparatus .heretobefore used is that known as the discipelletizer. A disc pelletizer |the finished pellets are not uniform in size and the rolling granular material by joining thenes together to yform larger spherically shaped particles, imparts arolling and l cascading action to the dampened rfine material. lIt has been `known heretofore to introduce pulverulent material andvwater into arotary drum for thefpurpose of clustering the pulverulent ymaterial, ,into larger masses. Such masses aresoft, irregularv in shape and size, and possess insuicient mechanical strength for further handling and processing. f

-A large number of process variables are involved in agglomerating fine material into pellets. vWhen individual particles are subjected to rollingaction inV a pel- -letizerto form spherical bodies the force of gravity can apply a large pressure tothe small particles on the surface actionis poorthus resulting in soft pellets having an -insucient mechanical" strength. The use of a.core pel' suffers from similar disadvantages.

It is an object 'of this invention to formballs or pellets of a predetermined s ize which balls possess sutl'cient meletizer has also been proposed, but this type of .apparatus chanical strength to be handled without disintegration by :novel apparatus for processing pulverulent'material into f I ..shape of a truncated cone'in which the back wallof the ofthe spherical body. As the spherical bodies come intoY intimate eontact, some of the uneven edges may vbe broken off thus creating fines to fill invoid spaces on other spherical bodies. 'It is commonly believedthat the particles are heldvtogether by capillary attraction caused by Water inthe wet bodies coupled with molecular adhesion z justed to the most desirable value if optimum results'are to be obtained., These variables'include the .retention time within a given machine whichis a Afunction of the slope and the feed rate, the speed of revolution ofthe machine, thepreparation ofthe miirbefore balling, andv the'correct design of the machine inorder to obtain the best action for ba-lling or pelletizing.

For a ygiven machine, theholdingcapacityand thence, the retention time at a given feed-rate changes with lthe slope of themachine. The greater the slope, the smaller the retention time land vice versa. For a ugiven machine at a constant slope the retention time varies with'the feed necessary to adjust the slope .of the pelletizing drum so that the pellets are' retained for the proper period, of time.,y

For example, if pellets withdiameters between the limits of to 1 /2 `inch are desired, too long a retention time may cause the `formation of pelletshaving diameters greater than v1/2 `inch and too short a retention time may causei vthe formation of pellets which do' not grow large enough to meet the inch lower limit.

The speed of the machine must also be adjusted for proper action.v The walls must revolveat a speed which will give the material a gentle rolling and cascading action to promote the continuous growth of balls or pellets by picking up fines as the balls roll across the iine'particulat'e feed material.

The most common pelletizing drum heretofore used standard 'equipmen such as conveyors,l screens, etc. In accordance 4with-the invention there is provided a balls or pellets. The apparatus comprises a` drum in the vdrum is formed as the base of the truncated conical mem ber. The small end of the truncated conical member is" open for discharging pellets. Incoming feed is introduced through the centerof the opening by means of afeed'con- I 'veyo'i".v The'ydrum operates on a slope of from 15 -35 Lupwardsffrom vthe horizontal, and preferablythel slope shouldv be vabout 25 lThe'dimensionsof thedrum are such that the ratio of the depth of the drum, to the large diameter ofthe' base, to 'the small diameter of the open end is 0.35f0.80:l .0 :0.500;90 and preferably this ratio isabout 06:1.0:0.7 5. v'The vangle which'the sides of the conical member form vwith the base of the member should be between about 70 and 90 ajnd'is preferably about 78. l

Attached to the v'open end of .the drurnisa concentric f lielically woundl screen, the strands of which are spaced apredetermined distance apart, for example,l approximatelyf-l/z'inch.l A. lifter cone is provided'fto catch the oversize pellets' (greater than inch) as they roll off the 1/2. inch screen. A second screen, forexample, a 1%; inch helically Woundscreen- Ais .concentrically arranged yaround `the. /z inch screen. These screens can be replaced with any size screen which will give the desired top and-bottom sizes. For example, a oneinch'screen and a 7/s inch screen can be substitutedforfthe l/z inch and 3/s inch rate. The faster the feed rate','the shorter is theretention time. A long retention time is desirable because the size 'fof the-balls thus produced can thereby be increased, however, when pellets of a particular size are'de-sired, it is screens or 1A inch vand 1A; inch screens canalso be used. The lifter cone isprovided with lifts which raise the oversize and `undersize'material and 'drop both into a chutewhich returns the material. to the feed conveyor and thence back into the pelletizingdrum.

Pellets of the predetermined desired size, for eirample, .Vz and inch pass through the V2 inch screen and are retained on the 1%; inch screen to be then passed'to a'frustoconical roll dryer fromwhich the finished pellets arepassed todischarge. A hot air duct is provided to force hot air through the roll dryer to at least partially dry the pelletsbefore they are discharged.

The geometric'shape of theV pelletizing drum is preciselysuited to uniform pellet formation and is designed to produce a better rolling action thanis accomplished by other knownpelletizers.' This better rolling action eliminates to a great extent the Vfree travel period that occurs in equipment s'uch as -the disc pelletizer during which the pelletsare carried up without any rolling.

' proximately 37.

The truncatedconc with the small discharge end holds larger' quantities of material than is possible in other equipment thus providing a longerrctention time than other revolvingcquipment of equal size.

The large volume of material being processed results in a great depth of material, and a long chord across the rolling face creates yan excellent rolling action in which some of the pellets are rolled down' over others which are rolling up. The-weight of material on top tends to hold the material underneath in a wedge-like position against the sloping base and side wall which form an angle of approximately 78 so that each particle is carried farther up on each revolution than it would be in vother known pelletizers. As the balls or pellets are being carried up, some are also rolling. When they reach the top, they cascade back down again. .Because of the greater depth of material andthe larger number of balls more Vforce is applied at each point of contact between the 'balls or pellets as they travel up and those travelling down. In addition,these" points of contact are more numerous. Pressures are thereby created on the surtace of the lballs which are many times greater than they would be if there were only one layer of balls resting or rolling'on a movi ingsurface as, for example, in-a ycommon cylinderdrum.v

Because the material is wedged into the pelletizer as itvk travels upward, the drum does not have' tosubject each particle to a high centrifugal force to keep it from slipping down. Therefore the peripheral speed of the pelletizing drum can be only abouty V2 thatpfother pelletp izers resulting in a reduction in operating cost. -Because 4 grindings. glass grinding fines, shale. red dog. zinc. vanadium, limestonephosphate rock, chronic orc linea'.

4iron concentrates. certain ceramic fines` chromium and tion. of the present preferred embodimcntthereofdescribed with refcrcnccto the accompanying drawings in which:

.FIGURE l is a plan view of the pelletizing and sizing drum` o f the invention. and

FIGURE 2 is across-sectional elevational view of the l apparatus shownon lines 2-2 of FIGURE 1.

Referri'rtgto the drawings, it will be seen thatvthe illustrated apparatus embodying the invention comprises a drum 10 in the shape of a truncated c onetin which the back 'wall 12 of the .drum is formed as the basejof 'the conical member. T he'side wallf14 of the drum 10 ex- 'of the novel angularity and arrangement ofthe drum, the

tine material tends to be retained towards the hase of the drum while the fully formed pellets dischargeifrom the small diameter en'd of the pelletize'r by rolling their way up the wall which is vmaintained at a -slope of ap- Thc sized green further upgraded when they are passed' to the roll'dryer where warm air is passed across'the pellets. 'I fhe-air car-y ries away part of the' moisture thereby producing apar- 1^ tially dried upgraded pelletwhichis'easier tolnndleibecause it is stronger'and dense. .This'upgraded'pellet is discharged onto 'a conveyor which carries it to .sinteririg or heat hardening equipment such as-isshown in my co-pending-application, Serial No. 243,376, filed December. 10, 1962.

.pellets discharged from the drum areA tends from thebase 12 to lan open cnd-whichvforms the small en d ofthe truncated conical member. A.fecd conveyor .1,'6 supplies 'feed material to the drum 10. When material has been fed to the drum 1 0 the drum isrotatcd by suitable means such as drive means l18 and drive shaft 20 which in turn -are driven by suitable means such as variable speedmotor' 21.

Asthe drum rotates. .pellets are formed which pellets tend to roll upwardly along' the wall 14 ofthe drum 10 and discharge through the mouth 1.5 of the drum onto a vhelically wound screen 22 operatively attached to. the mouth end 15 of the drum 10. The strands of the screen 22'are spaced zii-predetermined distance apart so that oversize pellets; (those which are larges than the predetern i'ined `size)-rema in upon the helically'wound screen 22 and are discharged'from said scree'n into lifter cone 24.

The oversize and undersize material discharges `in to the V lifter cone. which has a slope of between 25 'and 75'. 4The lifter cone is` provided withperipheral litters which pick the material -upto a point betweenl oclock and 2 oclock at which point the force of lgravity causes the material to fall down vonto agehute which leads the material'to the feed conveyor belt. It is then carried' into the drum v along with the new feed. The head end of the conveyor feederhas' an adjustable roll Crusher thereonwhich is driven by the head pulley and the oversize material is The lifter cone 24, is open-ended and is formed in lthe shape of afhtruncated conicalmembcr, the small end of the lifter cone 2 4 faces' towards the d rum10 The base of the lifter cone isV provided with a peripheral inwardly facing tiangciZ/to catch anymaterial falling into the lifter cone, Lifters 28-arc spaced aroundthe periphery of the lifter cone at the juncture between the lifter cone l24 a rtd its flange`26;I As material falls into the lifter cone 24 it rolls un'til'it reaches the lifters 28 `which then lift the material to -a position between l oclock and 2 o`clock at "'whic h point gravity causes the material to' .slide otfthe litters 28 and fall into 'ch'ute 30 which leads themat'erial back 4to the feeder belt 16 on which'belt the material is returned to' the drum 10.

thereby crushed. The rolls are vset slightly closer than the predetermined top size thereby crushing all oversize pellets and returning them directly intoI the pelletizer drum without the necessity of a special recirclulating'conveyor.H l The desired pellet size (e.g., -1/2 `inch) can 4 be programmed into the screens and because of the "design of the a-ppartus and the shape of the truncated cone, the drum will produce pellets of a desired size substantially constantly without any substantial amount of materialpassing into 'the lifter cone for'recirculation. The pellet size can be controlled by slight changes inthe slope, speed,

feed rate, etc.

Exemplary of the known tine materials that have been successfullyl pelletized in the novel pelletizing drum of this invention are: basic oxygen furnace dust, bauxite, iron ore fines, iron oxides. copper fines, the non-magnetic fraction of `y ash such tas 'from steam generating plants, the magnetic fraction of y ash, stainless steel distance 4between the-strands of the screen 22 pass through the screen 22 andtdrop onto a second concentric screen 32. Screen 32 is helieally wound and comprises strands wound a predetermined but smaller distance apart than thestrands of'screen 22. Any fine material discharged from the drain' l()` will pass through both screens 22 and 32. vUndersize material passing through screen'32 falls into the lifter cone'24 and is recycledv along with the oversize material from screen 22. Pellets having a size between the predetermined sizes of the screens 22 and 32 for example, -1/2 -l-'-Vs inch material falls through screen 22 and is retained on screen 32.l The material then rolls from'screen 32 onto a roll drying screen 34 which comprises perpendicular strands spaced Va inch apart. These product pellets which pass to roll drying screen 34 roll thereon and are discharged onto a belt conveyor 36 which carry the pellets to sintering or heat hardening .equipment for further processing.

While the sized green pellets are rolling on the screen dryer 34 warm air is passed therethrough and across the tothe materialtherein to aid in balling the mater A screens mounted adjacent thereby producing a partiallydry pellet which. is casier to handle because it is stronger and denser;v T hel warm air is passed vthrough screen dryer 34 by means of a blower 38 and hot air duct 40. t y

The entire apparatus including the drum 1 0, screens 2.2, 32, lifter cone 24, and.l roll dryer 34'.rotate together as the drum is rotated bymeans of drive 1'8. The lifter cone 24 is supported and rotates on idler roll'42 and the entire structure is supported by structural zsupports f I' In operation, feed material is passed into druml 10 by means of feed conveyor 16'. `Drum' 10 is rotated by drive meansk 18 and drive lshaft 20 which in turn are driven by variable speed motor 21. The material in the drum' is caused to roll andcascade. therein thereby form- CII a lpredeterr'nined size from 'said sizingscreens, and means to pass air through'lsaid roll .dryer to dry said size pellets. 3. Apparatus for the production of pressure hardenedy pellets from pulverulent material comprising, a rotatably mountedl truncated conical drum membery for forming pellets from said pulverulent material, said drum member.

. having a base forming l,the vbalrvvall of thendrum, a' side ing pellets. To aid in the formation of pelletsI water y Sprays (not shown) may be positioned within the drum 10. As the pellets are formed they ride upwardly along wall 14 of `drumv10 and are discharged onto helically wound screen 22;v Oversize material is retained on 'screen' 22 anddischa'rged therefrom intolifter cone 24g; Under# size material passes t-hrough screen' 22 and screen' 32 and Iundersize pellets, a feed, conveyor for said drum," i

wall, and an open upper end,a` pairof concentric sizing Screens mounted adjacent the open .fend of `said' drum to'separate oversize and undersize pellets 'from-f pellets o fa predetermined size, aconcentrically arranged truncated Vconical lifter means .for receiving said oversize andfundersize pellets from'said sizing screens,,said. 1ifter means being mounted adjacentv the-open end ofsaid drum, lifting members 'circumferentially arranged-f around the periphery of said lifter means for liftingv said oversize and means to recycle materialfrom saidvlifter means and isalsov discharged into lifter -cone 24. The properly sized pellets pass through screen 22 and are"l retained o n screen 3.2,to'be discharged onto roll dryer 34 where y warm air is passed over the green pellets. lThe partially f;

dried. pellets are then passedft'o belt conveyor 36 fory further processing. VThe oversize and undersize material passinginto lifter cone 24j1iS -liftedby lifters l28 and dropped in chutefrom whence they aredischarged onto feed'conveyor 16 and recycledto thegdrum 10. The'- material on feedconveyor`16 is passed throughcrushing t r'olls"17 wherebythe 'oversize :materialv is crushed, anda l the feed and recirculatedymaterial is then dropped into.

vthe drum 10. Whennecessary a water 'sprayff('iiot'shown)/ ymay be located within the drum l10 lto add m risture ral.

1. Apparatus for the productionv of pressure hardened peIletsfr-om'pulverulent material comprising", -a rotatably'A y mounted ltruncated -coriical drum'mem'ber.'.for forming pellets from sa-id. pulverulent materia-1,'said drum ymein-' ber having'a base forming the backwallofthe drum,

a side Wallfandan open upper end, said. drum being mounted'at an angle' of between about `l5 and 35 u.p"

wards from the horizontal, the ratio of, the. length. of

said sidel wallof 'said drum to the diameter of said base tothe diameter of said open end beingl about G-0.801` 1;()2050-090',

separate oversize and undersize pelletsfrom pellets 'of 1 a predetermined size, a concientricall'y arranged truncatedvconical lifter means for receiving said oversize and v uridersize pelletsfrom said sizing screens; said liftermeans' being mountedadajacent the open'end k of saidv drum `and having a largerydimeter thana'nd surrounding said sizing screens, ,lifting members circumferentially;.positioned around the `periphery* of said lifter means for Yliftl a ing said oversize'andundersize pellets, a vfeed conveyor for said drum, chute means to 'recycle material fromv said lifter means to vsaid feed conveyor, a roll. dryer con.

centrically mounted around said drum and adapted to rec'eive said pellets ofapre'determined size from said sizing lscreens, and means to `pass air through said vroll Adryer to partially dry said sized'pellets.

2. Apparatus for the production of pressure hardened a pair of. '-conc'erit'ric sizing the openendof saidkdrumto,

f'to saidffeedfconveyor.

pelletsfromsaid pulverulent material, said drum meml ber having a'base forming the back wall of the drum, a side vwalljandk'x open upper,. end,a pair of concentric sizing screens .mounted adjacent the open end of. said drum to separate oversize and undersize pellets frompellets-of a predetermined size, a' concentrically arranged truncated conical lifter means for receivingv s aid oversize f aridunder'size pellets from said sizing4 screens, said lifter chute 'means to recycle n iaterialy from said lifter means roll-dryer.' u

mounted truncated `'conical""dru'm member for forming- .pellets from'ysaid-.pulverulent materialv s aid drum member "having a base forming-the back wall of the drum, a side walla'ndan open upper end,l said drum being mounted v atari-angle of between about and 35 upwardsfrom 'thehorizontalg apair; of concentric sizing screenSQmoun'ted. adjacentjth'e"open end o f said drum to separate oversize and unders'izfe 1'pellets from pellets-. of a predetermined size, a concentrically arranged; truncated conical lifter,

means-for receiving saidj oversize and undersize peilets from v said sizing screens, j adjacent the open end of said drum, and said lifter means `having a larger diameterthan and surrounding said sizing l screens,- lifting 'members i'ci'rcumferentially arranged "around lthe periphery otvsaidlifterv means for lifting .said

, oversize andundersize pellets, a feed conveyor for said drum, chute means to recycle material from saidv lifterf fmeans to'said feed Conveyor, a vroll dryer concentrically pellets from pulverulent material-comprising, a rotatably'v mounted'truncate'd conical drum `member for forming pellets yfrom said pulverulent material, said drum member having a base forming' the back wall o f the drum, a side wall, and an open upper end, -a pair of concentric-sizing screens mounted adjacent theopen end of saiddrumfto separate-l oversizeand undersize pellets from pellets of a predetermined size, a roll dryer concentrically mounted l around said drum and adapted to receive said pellets of `shape of ajtruncatedcone said truncated said Alifter Vmeans 'being mounted pellets of `a predetermined size from said sizing screens, and means to' pass air through saidv roll dryer;

`mounted around said drum and adapted to receivesaid 6. Apparatus-for theproduction of pressure hardened pellets from pulverulent material comprising `a rotatably mounted 'drum member-.formed substantially in v the cone having an axis of rotation, a closedbase, an open upper end smaller than the siz'e of said base, ,and saidbasetofsaid open upper'end, the diameter ofsaid ldrum member diminishing from said closed'base to said nopen upper en d at a substantially constant rate', and

.. saiddrum member being mounted with its axis of' rotation -at anl angle of from 15 to 35" upwards from the horizontal.A 7. Apparatus for the production of pressure hardened 4. Apparatus for the production caf-pressure hardened pellets from' pulverulent materialgcornprising, a rotatably v 1 mounted truncated conicalLdrum member for forming l5. Apparatus `for the 'i production ,fof pressure hardenedpellets fromjpulverule-ntmaterialfcomprising, va `rotatably asidewalltextendingfrom.v v

7 pellets from pulverulent material comprising a rotatably mounted drum member formed substantially in the shape of a truncated cone said truncated cone having an axis of rotation, a closed base, an open upper end smaller than the size of said base, and a side wall extending from said base to said open upper endthe diameter of said member diminishing at a substantially constant rate from said base tosaid open upper end, said drum member being mounted with its axis of rotation at an angle of from l5 to 35 upwards from the horizontaland the ratio of the length of said side Wall of said drum to the diameter of said base to the diameter of said upper end being about 035-080:1.0:0.50-0.90.

8. Apparatus for the production of pressure hardened pellets from pulverulent material comprising a vrotatably mounted drum member formed substantially in the shape of a truncated cone said truncated cone having an axis of rotation, a closed base, an open upper. end smaller than the size of said base, and a sidewall extending from said base to said open upper end, the diameter of 8. said drum member diminishing from sad'closedbase to said open upper end at a substantially con'stantrate, a roll dryer eoncentrically mounted around said drumand adapted to receive pellets from said drum,` and means to pass air through said roll dryer to dry said pellets.

References Cited by the Examiner UNITED STATES PATENTS 2,709,833 6/55 Wiklund '18-1 2,828,190 3/58 King 2- 18- 1 2,843,043 5/58 Haley et a1 18-1 3,040,375 6/62 Rowen T 18-1 FOREIGN PATENTS 517,192 10/55 Canada. 498,469 '9/54 Italy.

WILLIAM J. STEPHENSON, Primary Examiner; 

2. APPARATUS FOR THE PRODUCTION OF PRESSURE HARDENED PELLETS FROM PULVERULENT MATERIAL COMPRISING, A ROTATABLY MOUNTED TRUNCATED CONICAL DRUM MEMBER FOR FORMING PELLETS FROM SAID PULVERULENT MATERIAL, SAID DRUM MEMBER HAVING A BASE FORMING THE BACK WALL OF THE DRUM, A SIDE WALL, AND AN OPEN UPPER END, A PAIR OF CONCENTRIC SIZING SCREENS MOUNTED ADJACENT THE OPEN END OF SAID DRUM TO SEPARATE OVERSIZE AND UNDERSIZE PELLETS FROM PELLETS OF A PREDETERMINED SIZE, A ROLL DRYER CONCENTRICALLY MOUNTED AROUND SAID DRUM AND ADAPTED TO RECEIVE SAID PELLETS OF A PREDETERMINED SIZE FROM SAID SIZING SCREENS, AND MEANS TO PASS AIR THROUGH SAID ROLL DRYER TO DRY SAID SIZE PELLETS. 